Hello, same story here, using gcc 11.2.0 on gentoo system with a fresh clone of nextRelease branch. It does not compile , even with -std=c++14 instruction, I had to use the trick provided by Christoph to get it compiled.
Replaced the broken opencascade-6.3 by opencasc...
app-text/dgs: fix + modifs thanks to Olivier Huber
sci-libs/gmsh: small corrections + version bump...
sci-libs/med: Version bump + corrections, doc a...
sci-libs/cgnslib: fixed DEPEND and RDEPEND conf...
sci-libs/gmsh-9999: removed keywords
sci-libs/med-2.3.5 needs >=sci-libs/hdf5-2.6.4